1. Field of the Invention
The present invention relates to an object detection apparatus, with a light emission device and a light reception device, for employing the wavelength in a solar absorption zone in a light spectrum extending from a visible radiation band to a near-infrared radiation band.
2. Description of the Related Art
Several techniques have been proposed for employing light to calculate an observed point viewed by a crew member in a vehicle. Generally, a light emission device is used to irradiate the eyes of the crew member with a specific light beam, and a light reception device is used to receive images reflected by the crew member""s retinas and corneas, so that the direction of the individual""s line of sight can be determined and the observed point can be calculated. An observed point calculation device intended for use in a vehicle, which is disclosed in Japanese Unexamined Patent Publication No. Hei 7-35543, calculates the position of the observed point viewed by a vehicular operator, without any physical contact being required. This device calculates the observed point by employing the fact that when the eyes are irradiated by a near-infrared beam, the luminance of the reflected retinal image depends on the distance to the observed point of the eye. First, for calibration, an image of the eyeballs is recorded by a pickup camera each time an imaginary image at a predetermined distance is moved. Information concerning the images reflected by the retinas and the corneas is extracted from the obtained image data, and the brightness of the images reflected by the retinas is calculated and stored. At the next calculation performed for the observed location, the position of the observed point is calculated by using the brightness of the images reflected by the retinas, and the direction of the line of sight is calculated by using information obtained from the images reflected by both the corneas and the retinas. In this fashion, the calculation of the position of the observed point is performed.
According to this method, in the daytime, when the face or another portion of the head is irradiated directly or indirectly by sunlight, the sunlight acts as a disturbance, and an image obtained by the reflection of the beam that is radiated by the light emission member is blurred because of the adverse affect of the sunlight. That is, when the quantity of the incident light produced by sunlight having the same wavelength as that of a beam radiated by a light emission member is equal to or greater than the incident light produced by the beam produced by the light emission member, the S/N ratio (signal-to-noise ratio) is drastically deteriorated, and the reflected image obtained using the light from the target light emission member can not be identified by using the light reception results.
An operator pickup apparatus disclosed in Japanese Unexamined Patent Publication No. Hei 7-134800 can obtain clear reflected images from the retinas of an operator by providing device for limiting the above described disturbance. The disturbance restriction device, such as a band-pass filter (B.P.F; an optical filter), is located along an optical path connecting the operator and a light reception device, so that a clear retinal-reflection image can be obtained even in the presence of a strong disturbance. An adverse effect produced by a disturbance that has a wavelength other than that of the beam radiated by the light emission member can be attenuated by using a band-pass filter; however, a disturbance producing light having the same wavelength as the light radiated by the light emission member will be passed through the band-pass filter, and as a result, will cause deterioration of the S/N ratio.
In addition, an apparatus that is disclosed in Japanese Unexamined Patent Publication No. Hei 8-159733 can determine the direction of the line of sight while ensuring the eyes will not be injured in the presence of a strong disturbance. Since in the presence of a strong disturbance the pupils are constricted, accordingly, a greater quantity of light must be emitted, and as a result, a problem concerning the safety of the eyes has arisen. Therefore, the disclosed device precisely determines the direction of the line of sight even in the presence of a strong disturbance, while providing for the safety of the eyes. The eyes of an operator are irradiated by an infrared ray so that the radiant energy density is equal to or smaller than a safety reference value, and so that the peak pulse power of the a light emission device is inversely proportional to the operating speed of a shutter; so that a reflected image is picked up in order to extract a reflected retinal image and a reflected corneal image; and so that the direction of the line of sight of the operator can be calculated from the positions of the reflected images. While the adverse effects produced by a disturbance can be reduced by increasing the shutter operating speed and the peak light emission power, the S/N ratio is not drastically reduced. However, the affect on the eyes due to the addition of the large amount of pulse light is unknown.
As is described above, when, to ensure the S/N ratio, the quantity of emitted light is increased until it is equal to or greater than the amount of incident light that acts as a disturbance, as does sunlight, a problem has arisen concerning the safety of the eyes when they are subjected to irradiation. To protect the eyes, a standard has been established to ensure that when the light emitted by an emission source is within a near-infrared irradiation band, its intensity should not exceed a recommended value of xe2x80x9c10 mW/cm2,xe2x80x9d as determined at a U.S. Labor Safety Conference. When the light emitted by a light emission source is within a visible radiation band, an operator may be dazzled by emitted light that exceeds the light beam in quantity and the operator""s eyes may be adversely affected.
It is, therefore, one object of the present invention to detect the state of an object at a high S/N ratio. It is another object of the present invention to provide an apparatus that is friendly to the eyes when detecting the line of sight.
To achieve the above objects, according to the invention, an object detection apparatus for detecting the state of an object includes: a light emission device irradiating an object with a light beam at a wavelength that produces less disturbance; and a light reception device including a filter through which to pass the light beam at the wavelength, and receiving a light beam reflected from the object. With this arrangement, the light emission device emits light at a wavelength that produces less disturbance, and the light is received by the light reception device after passing through the filter so that the state of the object can be precisely detected without the process being affected by any disturbance.
Disturbance is changed to noise when a reflected light is received, and in the daytime, sunlight acts as a representative disturbance. At night, all the lights in a town, such as the lights of cars, neon signs, or lights in shops and houses, act as disturbances.
In the above object detection apparatus, sunlight may act as the disturbance. That is, detection of the object is performed by using a light at a wavelength that has the low spectral radiative illuminance of the spectrum of sunlight. With this arrangement, sunlight at a wavelength other than that used for the detection of an object has no effect on the detection operation, and therefore, even in the daytime the state of the object can be precisely detected.
Further, in the above object detection apparatus, the object may be the eyes of an operator, and the object detection apparatus may be mounted on a vehicle so as to obtain reflected images from the retinas and the corneas of the eyes and to thus calculate an observed point viewed by the operator. With this arrangement, preferred reflected images of the retinas and corneas can be obtained, and the observed point viewed by the operator can be accurately calculated.
In addition, according to the above object detection apparatus, the wavelength may be a wavelength in a non-visible irradiation band. With this arrangement, since flicker due to light from the light emission device can be prevented, for example, when the detection apparatus is used at night, the state of an object can be detected without causing the eyes of a human being to be distressed.
Further, in the above object detection apparatus, the wavelength may be one of a plurality of wavelengths producing less disturbance. That is, since sunlight includes a plurality of wavelengths for which the spectral radiative illuminance is quite low, one of the wavelengths is selected in accordance with the environment in which the invention is employed. With this arrangement, since the environment is taken into consideration when a wavelength is selected, the state of an object can be precisely detected in accordance with the environment.
Moreover, the wavelength may be selected from a visible irradiation band in the daytime and from a non-visible irradiation band at night. With this arrangement, since wavelengths can be selected that are appropriate for the environmental conditions encountered in the daytime and at night, the state of an object can be accurately detected both in the daytime and at night.